/// Conditional input pin trait.
///
/// Used for conditional requirement of the [`InputPin`](::embedded_hal::digital::InputPin) trait based on the `ack` feature.
/// - Every [`InputPin`](::embedded_hal::digital::InputPin) implements this trait, if the `ack` feature is enabled.
/// - Everything implements this trait, if the `ack` feature is not enabled.
const _: = ;